a) Field of the Invention
The present invention generally relates to electronic musical instruments, and more particularly to an electronic musical instrument having a performance manipulator capable of generating control variables which change substantially continuously, such as a variable which represents a position on a line or on a plane.
b) Description of the Related Art
Most of electronic musical instruments employ keyboards as main performance manipulators. A keyboard has a plurality of keys so that information of pitch corresponding to each key is generated when the key is depressed.
Recently, much headway has been made in the development of electronic musical instruments capable of imitatively generating musical tones of a rubbed string instrument, or the like. In a rubbed string instrument, pitch is changed continuously by shifting the position of the finger pressing a string on a fingerboard. Further, the rubbing speed of the bow, i.e. relative speed between the bow and the string (bow speed) and the pressure of the bow which is applied to the string (bow pressure) can be changed continuously, so that the musical tone can be changed expressively correspondingly to the amounts of the continuous changes of these variables.
Also in an electronic musical instrument, use of such control variables that can change continuously is effective for changing the musical tone expressively.
Heretofore, performance manipulators such as a keyboard, a guitar-style controller, a wind-instrument style controller, etc. have been used as real-time performance manipulators for electronic musical instruments. However, the expression of the musical tone in electronic musical instruments using those performance manipulators is more or less inferior to that in natural musical instruments.
Therefore, there has been made an idea that the speed and pressure equivalent to the bow speed and the bow pressure in a natural rubbed string instrument such as a violin are detected by use of a real-time performance manipulator capable of imitating the image of the rubbed string instrument and are inputted as tone generator control parameters.
The assignee of this application has proposed various manipulators of one dimension (linear manipulators) or two or more dimensions (plane or space manipulators) having a pressure sensor. By actuating the proposed manipulators, it is possible to detect the position and pressure at every sampling time interval to thereby generate information pertaining to the speed and pressure.
The information pertaining to the speed, pressure, etc. given by such manipulators capable of generating control variables which can change substantially continuously, contains various kinds of noise. For example, the noise is caused by the variations of the detecting means per se, etc. and by the disturbance, etc. When such signals containing noise are inputted into tone generators, the tone may often become unstable or may often stop.
For example, a non-linear characteristic of a non-linear circuit 18 which is incorporated in tone generator 60 (FIG. 2) is shown in FIG. 15 and behavior of the characteristic is hereunder described.
The non-linear circuit 18 is accompanied with a division circuit 17 provided on the input side, and a multiplication circuit 19 provided on the output side. The division circuit 17 and the multiplication circuit 19 receive the bow pressure signal through the gate 20. That is, a small signal formed by dividing the input by the bow pressure signal is inputted into the non-linear circuit 18, and a large signal formed by multiplying the output by the bow pressure signal is produced in the multiplication circuit 19. Accordingly, when the characteristic of the non-linear circuit 18 is fixed, the scales of the input and output signals of the non-linear circuit 18 change as the bow pressure signal changes. In short, as the bow pressure signal is enlarged, the linear region of the characteristic is widened. This means the fact that the static friction coefficient portion is widened.
When the input signal is small amount, the output signal proportionally increases. Then, the output signal is fed back through LPF 22 to be applied to the input signal is an adder 15. So, the input signal to the non-linear circuit 18 increases by a feed back amount, the output signal responsively increases. In this manner, the output signal gradually increases. Finally, the input signal excesses a certain value, i.e. the input signal reaches the small output region, then the output signal falls into small amount. Therefore, the feed back amount into the adder 15 also falls into small amount. Responsive to this, input signal to the non-linear circuit decreases, i.e., the input signal becomes to get into the linear region.
If bow motion is sustained, the input signal is gradually increases, above-mentioned increase-decrease motion is repeated. As a result, the non-linear characteristic simulates relative motion between a bow and a string.
But, if the input signal rapidly increases, the input signal into the non-linear circuit 18 may directly jump into the small input region from the linear region without gradual increase. Therefore, the above-mentioned motion is not functioned, so precise simulation of the natural musical instrument is not realized.